Im also searching web on changing font of text in text layer of photoshop cs5. System font are easily changed but not embedded fonts. Im trying to develop plugin that can use web fonts which will load dynamically.

I think it is only possible to use fonts in Photoshop that are installed locally. So your plugins would need to download and install the font before it can be used in Photoshop. To change the font of a text layer you need to develop an automation plugin.

Alternatively make your plugin render the font and the text yourself as a bitmap layer. Then you have full control and do not need to install the font on the user's machine.